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TheU Physician and Sportsmedicine U December 1994 Superficial Heat and Cold – How to Maximize the Benefits The wide array of superficial heat and cold modalities offers physicians many options for treating sports-related injuries. Appropriate application of heat and cold therapies can reduce the impact of an injury by relieving pain, reducing swelling, and encouraging rehabilitation. By: Matthew P. Kaul, MD and Stanley A. Herring, MD Superficial heat and cold techniques are well entrenched in the therapeutic strategies of healthcare professionals who treat sports injuries. These adjunctive therapies, which exert their effects at depths of 1 to 2 cm, are most effectively used in comprehensive rehabilitation in a manner that limits tissue damage, controls symptoms, and returns the injured part to optimal function. To safely maximize the benefits of these modalities, it is useful to review application principles and to employ a variety of heat or cold therapy options. What can superficial heat do? Superficial heat increases tissue temperatures to varying degrees. It has also been shown to increase the extensibility of collagen tissue, reduce muscle spasm, produce analgesia, produce hyperemia, and increase metabolism. (Deep heat is also an important form of thermotherapy.) Increased tissue temperature depends on the depth and type of the tissue. A “cooling reflex” was initially reported in classic studies by Hollander and Horvath (1) which knee intra-articular temperature dropped with less than 20 minutes of hot pack heating. This principle has since guided treatment recommendations (2). However, recent investigators have failed to reproduce this “cooling reflex” and found that superficial heat rapidly increases intra-articular knee temperature. These investigators (3,4)question the wisdom of heating inflamed joints. Increased tendon and joint capsule extensibility with superficial heat has been thoroughly studied (5). Prolonged static stretching of a tendon with or immediately after heating can elongate the tendon. Heating at therapeutic temperatures does not significantly lesson tendon strength. Muscle spasm reduction occurs through direct and indirect reflex effects, predominately the latter (6). Secondary afferents in muscle are responsible for the tonic phenomenon assumed to be involved in secondary muscle spasm. Most secondary afferents slow their firing when heated, which presumably decreases muscle spasm. Additionally, Golgi tendon organs, which inhibit muscle contraction, increase their firing when heated. Heating of skin has also been shown to decrease the activity of gamma fibers (the efferent component of the muscle spindle) through reflex effects. Analgesia production occurs because heat reduces painful secondary muscles spasm, acts as a counterirritant, and possibly stimulates endorphins. A number of studies (7) have 1 Kaul, Matthew MD & Herring, Stanley, MD documented that heat increases the pain threshold when applied to a peripheral nerve, to skin, or to free nerve endings. Heat produces pain and tissue damage at tissue temperatures of 113 F (45 C). Increased blood flow occurs through heat’s reflex and direct effects. Heating has a direct effect that relaxes the smooth muscles of vessel walls. Vasodilation may result from a release of inflammatory mediators and from heat’s effect on axon reflexes (6). Increased blood flow removes most of the heat applied to skin, leaving little heat to reach deeper tissues. Muscle blood flow is minimally affected by superficial heat. Heat inhibits experimental inflammation (8) but clinical studies are unavailable. Increased tissue metabolism occurs with the initial rise in temperature, though muscle metabolism decreases with prolonged vigorous heating, perhaps because heat-sensitive enzymes are destroyed. Increased collagenolysis has been found with increased intra- articular temperatures, (9) which has implications for joint integrity. However, Mainardi et al (10) did not find progressive joint destruction with daily heat therapy (electric mitten with maximum temperature of 104 F (40 C)) in patients who had rheumatoid arthritis of the hands. Effective Heating Strategies Perhaps the main benefits of heat therapy are to reduce muscles spasm, produce analgesia, and increase flexibility. In many instances, the modalities are therefore used at the post- acute stage after initial pain and edema have subsided. However, heat is often the initial treatment for chronic conditions. Because each patient’s needs will vary, it’s helpful to keep in mind certain considerations when selecting the appropriate heating technique. Techniques include heat packs, paraffin wax, fluidotherapy, hydrotherapy, and radiant heat. Laser treatment has been used to promote wound healing and to treat arthritis and myofascial pain syndromes, but its use remains controversial. (11) Determine if the patient’s injury needs vigorous or mild heating. Vigorous heating is generally reserved for chronic processes, which are aided by increasing the extensibility of connective tissue, maximally increasing blood flow, or reducing muscle spasm. Vigorous heating is contraindicated for acute inflammation. The therapeutic tissue temperature for vigorous heating is 104 F to 113 F (40 C to 45 C), and the duration of tissue temperature elevation is 3 to 30 minutes. Mild heating is primarily used to treat acute and sub-acute injuries, though it is contraindicated for certain serious acute injuries such as a sprained ankle. Mild heating can reduce muscle spasm in an acute back injury, help resolve tissue inflammation, and reduce pain. The goal of mild heating is to increase tissue temperature to less than 104 F (40 C). Methods of achieving mild heating include using modalities known to produce mild effects such as dip paraffin, or employing heating modalities at reduced output or for shorter times. Understand heating patterns For vigorous heating, the highest temperature needs to reach the site of tissue injury. For example, ultrasound vigorously heats the hip joint but only mildly heats superficial structures such as skin and muscle, whereas superficial heating agents cannot vigorously heat deep joints. Three main factors affect temperature distribution in tissue: the amount of energy converted to heat at a specific tissue depth, the thermal properties of the tissue, and the modality used and its method of application. 2 Kaul, Matthew MD & Herring, Stanley, MD Most superficial heating agents significantly heat skin and subcutaneous tissue, but not deep joints or muscle deeper then 1 to 2 cm. However, superficial heating with a heat mitten (set at 104 F (40 C)) has been found to increase metacarpophalangeal joint temperature from 89.6 to 103.1 F (32 to 39.5 C) (10). In the knee, a joint of intermediate depth, Oosterveld et al (4) found that 10 minutes in a paraffin bath increased intra-articular temperature by 6.3 F (3.5 C)—to 96.8 F (36 C), the temperature needed to increase enzymatic activity (9). In a study of wet and dry heat, Abramson et al (12) found that patients tolerated dry heating better than wet heating. When compared with dry heat at similar temperatures, wet heat produced significantly higher skin, subcutaneous, and muscle temperatures. However, when dry heat was applied at greater temperatures than were comfortable with wet heat, the same effectiveness as wet heat was demonstrated. Consider contraindications Because pain is a critical warning sign of tissue injury, heat therapy is contraindicated at sites of decreased sensation and when the patient’s mental status is altered. A bleeding diathesis is a contraindication because heating increases blood flow and vascular permeability. Heating over malignancies is contraindicated because it can accelerate tumor growth and metastasis (6). Heat should not be applied to the gonads or to a fetus. Tissues with inadequate vascular supply should not be heated because increased metabolic demands can lead to ischemic necrosis. It has been recently shown that in diabetic patients with neuropathy, skin blood flow decreases during local heating in contrast to patients without diabetes and patients with diabetes but no neuropathy. (13) These factors decrease the skin’s ability to dissipate heat and probably increase burn risk. Select the best modality Choosing the appropriate superficial heating method depends on the shape and area to be treated, the depth of target tissue, whether concurrent exercise is desired, the duration of treatment, as well as more pragmatic factors such as expense and ease of application. Examining cold benefits Superficial cold lowers tissue temperature to varying degrees. It also can produce analgesia, reduce edema, decrease muscle spasm, and reduce metabolic activity. Analgesic effects are mediated by cold’s effect on nerves and nerve endings, by its counterirritant effects and by reduction of metabolic activity (6). All nerve fiber types are affected by cold; small myelinated (pain) fibers are affected first, then large myelinated fibers, then unmyelinated fibers. Nerve conduction velocity decreases proportionately to decreasing temperature. Cooling below 68 F (20 C) reduces acetylcholine production. Cold also increases the time of the verve’s recovery cycle after excitation and increases the refractory period (6). The analgesic effect of cold is often used to facilitate activity in an injured limb. However, caution is advised since the analgesia may allow the patient to exceed a desired activity level and cause unwanted tissue damage. In certain instances,

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